(101c) A Design for Circularity Strategy Is Not Always Environmentally Beneficial: Shifting from Aluminum to Steel Frames for U.S. Photovoltaics Modules

The design for circularity (DfC) strategy reduces a product's environmental footprint by adopting environmentally benign design and material choices. The transition from aluminum to steel frames in photovoltaic (PV) manufacturing is being increasingly adopted [1],[2],[3] as an environmentally beneficial DfC strategy, as primary steel has an 86% lower climate footprint than primary aluminum [4], [5]. An additional significant concern with aluminum frames is China's near monopoly in their production [6]. These imported frames are notably carbon-intensive [7] and expose the US PV manufacturers to geopolitical-driven disruptions in supply chains. Consequently, the shift toward domestically manufactured steel frames not only addresses the environmental goals of the PV industry but also mitigates the supply-chain vulnerabilities within the PV industry. However, existing research has not yet assessed whether implementing the DfC strategy—specifically transitioning from aluminum to steel frames—would yield environmental benefits if secondary aluminum and steel sources are used instead of primary materials. This is particularly relevant given that secondary sources currently account for approximately 70% and 84% of total steel and aluminum production, respectively, in the United States [8], [9]. Moreover, one of the four primary aluminum smelters operating in the United States relies on renewable hydroelectricity, resulting in significantly lower carbon emissions associated with aluminum production [10]. Therefore, considering these region-specific factors in aluminum production, the environmental benefits of transitioning to steel frames must be carefully re-examined.

To this end, we present the first comprehensive lifecycle assessment (LCA) to evaluate the environmental tradeoffs between four material choices for PV frames – primary aluminum, secondary aluminum, primary steel, and secondary steel. For the primary supply chain, we account for 98 smelting plants, 15 frame manufacturing facilities, 36 module manufacturing facilities, and 4500 utility-scale PV installation sites. For the secondary supply chain, we account for 4500 PV decommissioning sites, 30 PV recycling plants, 2300 scrap collection facilities, 250 secondary smelting and refining facilities, and 15 frame manufacturing facilities. We also account for the inventory requirements, transportation distances, and electricity mixes used in the different processes in the primary and secondary supply chain (listed above). The chosen functional unit for this study is “1 m² of a solar PV module”. As the primary focus of this LCA is the structural frame of the module, normalizing to 1 m² of module area allows for eliminating the inconsistencies arising from the varying dimensions of PV modules commonly found in the industry.

Excluding transportation distances, the analysis reveals that incorporating DfC strategies can either increase or decrease the greenhouse gas (GHG) footprint of PV module manufacturing, depending on the material substitution. As shown in Table 1, replacing primary aluminum with primary steel or secondary steel leads to significant reductions in GHG emissions per square meter of PV module, with the most significant reduction (43%) achieved when secondary steel replaces primary aluminum. However, not all DfC-driven substitutions result in emission reductions. For instance, replacing secondary aluminum with either primary steel or secondary steel increases the GHG footprint of PV module manufacturing—by 32% and 6%, respectively

Furthermore, we explore the environmental benefit when the metal recovered from a recycled PV module offsets the primary production of that metal. In this scenario, stand-alone PV module recycling shows that modules with aluminum frames offer a higher net carbon benefit—11.3 kg CO₂ eq per m²—compared to those with steel frames, which provide 4.3 kg CO₂ eq per m². (Figure 1)

However, including transportation distances across the primary and secondary supply chains significantly changes the relative environmental preferences of the four material choices. The impact of the transportation distances is depicted visually through an environmental preference graph, which identifies cut-off points and bounded regions wherein a material is preferable to the other three alternatives. Using a geographic information system (GIS) analysis, we depict the environmentally preferable material alternative to manufacture frames for PV modules to be installed in utility plants across the US map based on the geospatial spread of the supply chain process for the four material alternatives. Furthermore, we demonstrate how DfC strategies have a policy implication by quantifying how the US-manufactured PV modules with frames made from the four-material alternatives either meet or fail to meet the ultralow carbon PV standards defined specifically for US PV manufacturers.

REFERENCES

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